Barack Obama's speech on race, delivered yesterday in Philadelphia, the city in which American democracy was founded and made concrete, was admirable, powerful, substantive and nuanced. That much is easy to know. What is harder to know, and what I do not know, is whether it will prove successful as a piece of politics.

He addressed head-on the firestorm over the incendiary and anti-American remarks made in a 2003 sermon by his former pastor at the Trinity United Church of Christ on Chicago's south side, the Rev Jeremiah Wright. Obama denounced Wright, making it clear where he disagreed with his spiritual mentor. The "profound mistake" Wright made in his most scabrous utterances, said Obama, rested in his assumption that "our society was static; as if no progress has been made; as if this country - a country that has made it possible for one of his own members to run for the highest office in the land and build a coalition of white and black; Latino and Asian, rich and poor, young and old - is still irrevocably bound to a tragic past."

But this was no facile "distancing" project of the sort politicians in extremis undertake to make a problem go away - for he embraced Wright as well. He is, Obama said, "like family to me". Say what you want of Obama; he did not take the easy way out here.

By longstanding tradition, the stage-crafted biographies of presidential candidates are presented to make Americans feel happy feelings about both candidate and country. Where possible, tales of heroism in battle are featured - see John McCain, John Kerry, George HW Bush et al.

Lacking that, the candidate and his handlers usually go for an up-by-the-bootstraps narrative, an immigrant success story - such as Michael Dukakis - or an account of a rise from the ashes of a broken home - one Bill Clinton. Lacking any of the above, some saga of personal redemption is offered - George W Bush flushed the whisky down the toilet and found Jesus.

In all cases, some small dose of adversity, some gesture towards the darker aspects of American life, is accepted. It is even demanded, because the point of introducing the gesture is to affirm the candidate's will and the nation's capacity to change. The 1988 Democratic candidate Dukakis's forbears faced discrimination; but they asked for no handouts and made it. Dole, who lost to an incumbent Clinton, came back from the second world war handicapped, lonely, a little embittered even, but he put himself back together and the greatest nation on earth allowed him to rise to great heights. That is the formula.

Obama's story does not quite hew to the formula. Or, perhaps, it does, but in a concentrated and intense form. His story asks Americans - specifically white Americans - to consider things about America that most of them would rather not. From this task, too, he was unflinching. He conspicuously did not speak of the "genius" of US constitution, as American politicians are meant to. He called the document "unfinished" and "stained by this nation's original sin of slavery", even making the founding fathers, whom he described as putting off for 20 years the decision on what to do about slavery, sound like regular old politicians.

I have to assume that many white Americans have been attracted to him in no small part because he seemed to offer a narrative that would not take us into these discomfiting, cobwebbed corners of the American psyche. He seemed, as someone's one-liner put it, "just the right amount of black"; like he probably belonged to a nice, genteel, interracial Episcopal church.

Well, tough - he didn't. And yesterday he basically told us why. He did so with about as much honesty as we have any right to expect from a person seeking the presidency. I am sure it helps us, as a society, to hear it all put out there with intelligence and subtlety. I am less sure about whether it will help him.